JPH0489844A - Production of crosslinked polyolefin molding - Google Patents

Abstract

PURPOSE:To produce a crosslinked polyolefin molding prevented from being deteriorated by ultraviolet rays by irradiating a molding comprising a crystalline polyolefin with ultraviolet rays of a specified wavelength at a temperature equal to or higher than the crystalline melting point of the polyolefin. CONSTITUTION:100 pts.wt. crystalline polyolefin is mixed with optionally 0.05-1 pt.wt. UV absorber (e.g. phenyl salicylate), 0.2-3 pts.wt. photosensitizer (e.g. 4-chlorobenzophenone), 0.3-4 pts.wt. crosslinking agent (e.g. triallyl cyanurate), additives such as an antioxidant, a filler, a blowing agent, etc., and the obtained mixture is molded into, for example, a cylindrical object such as a tube or a pipe or a flat object such as a film or a sheet to obtain a molding comprising the crystalline polyolefin. This molding is irradiated with ultraviolet rays of a wavelength of 200nm or above at a temperature equal to or higher than the crystalline melting point of the polyolefin.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a method for producing crosslinked polyolefin moldings by ultraviolet irradiation crosslinking.

"Prior Art" Known methods for crosslinking polyolefins such as polyethylene include radiation crosslinking using electron beams and chemical crosslinking using organic peroxides.

Radiation crosslinking is limited to thin molded products with a thickness of about 1 mm or less due to crosslinking efficiency and radiation transmission efficiency, and has disadvantages such as high equipment costs and dangerous operation.

Chemical crosslinking can also be applied to thick molded products, but crosslinking takes time and requires first crosslinking equipment for heating and pressurizing. Additionally, when extrusion molding or injection molding polyolefin compositions containing organic peroxides, some of the organic peroxides decompose and produce so-called scorch, which hinders long-term operation of molding equipment. Sometimes.

Furthermore, in the field of insulated wires, a 7-run crosslinking method is known. In this case, since the crosslinking reaction is carried out by reaction with water, if the thickness of the coating with the continuous wire layer is 3 to 4 mm or more, water permeation is slow and crosslinking takes a long time. Second, there is an inconvenience that a trace amount of moisture remains and the electrical characteristics are not sufficient.

On the other hand, crosslinking by ultraviolet irradiation has been put to practical use in the fields of ultraviolet curing paints and photorenost.

However, crosslinking of crystalline polyolefins and fins with polyethylene t by ultraviolet irradiation has not yet been put to practical use.

On the other hand, the present inventors have found that a crystalline polyolefin can be efficiently crosslinked with ultraviolet rays by first irradiating the crystalline polyolefin with ultraviolet rays at a temperature equal to or higher than its crystal melting point, and are proceeding with its practical application.

However, although mercury lamps, metal halide lamps, etc. can be considered as common sources of ultraviolet rays, the wavelength range of light obtained from these sources is about 150 to 600 nm. Among these, deep ultraviolet rays of 200 nm or less have particularly strong photochemical effects, and when irradiated to polyethylene, they have a strong effect of cutting the main chain and speeding up deterioration.

``Problems to be Solved by the Invention'' Therefore, an object of the present invention is to prevent deterioration of the crystalline polyolefin due to ultraviolet rays when crosslinking a molded article made of crystalline polyolefin such as polyethylene by ultraviolet irradiation.

"Means for Solving the Problems" In order to solve the above problems, the present invention irradiates a molded product made of a crystalline polyolefin with ultraviolet rays having a wavelength of 200 nm or more at a temperature higher than the crystal melting point of the crystalline polyolefin. It is something.

"Function" At temperatures above the crystal melting point, all of the crystalline portions of the crystalline polyolefin are in a molten state, resulting in good transparency. Therefore, the transmission efficiency of ultraviolet rays is greatly improved,
The crosslinking efficiency increases, and even thick molded products can be uniformly coated with a crosslinking reaction. Furthermore, by using ultraviolet light whose wavelength is limited to 20 Or+m or more, deterioration of the crystalline polyolefin can be prevented.

The present invention will be explained in detail below.

The crystalline polyolefin used in this invention includes:
There are ethylene copolymers such as polyethylene, polypropylene, polybutene], poly-4-methylpentene-1, and ethylene/propylene copolymers, among which are low-density polyethylene, high-density polyethylene, linear polyethylene, Polyethylenes such as ultra-low density polyethylene and ultra-high molecular weight polyethylene are preferred because they have high crosslinking efficiency. Of course, a mixture of these may be used.

This crystalline polyolefin, alone or preferably as a mixture with an ultraviolet absorber, is formed into a molded article by various molding methods. This mixture may be further mixed with a photosensitizer or this photosensitizer and a crosslinking auxiliary agent to form a molded product.In particular, the addition of the photosensitizer allows UV crosslinking to proceed efficiently. preferable.

The ultraviolet absorbers used here include salicylic acid derivatives such as phenyl salicylate, hensitriazoles such as 2(2'-hydroxy-5-methylphenyl) peptriazole, 2-hydroxyhenzophenono,
Hydroquinobenzophenones such as 2-hydroquino-4methoquinobenzophenone, 2-hydroquine-4octoquinobenzophenone, and 22'-nohydroquino-4-methoquinophenone are preferably used. For example, phenyl salicylate is optimal because it absorbs ultraviolet light of 320 nm or less. The amount of the second ultraviolet absorber to be blended is determined in the range of 0.05 to 1 part by weight per 100 parts by weight of the crystalline polyolefin.

If the amount is less than 0.005 parts by weight, the ability to prevent the deterioration of the crystalline polyolefin during ultraviolet irradiation will be low, while if it exceeds 1 part by weight, the UV deterioration can be controlled, but the irradiated ultraviolet rays will be absorbed by the ultraviolet absorber. This increases the degree of crosslinking, which reduces the crosslinking effect, which is undesirable.

However, as photosensitizers, benzophenone, 4chlorobenzophenone, 2-chloropenzophenono, 4.4°-
Hensiphenones such as nochlorohenzophenone and hexachlorohenosyphenone, chlorenodic anhytrite, and Sandry I 000 j (trade name, manufactured by Monosand Co., Ltd.) are used. The compounding amount of this photosensitizer is 02 to 100 parts by weight of the crystalline polyolefin.
It is preferable to add 3 parts by weight, and if it is less than 0.2 parts by weight, the effect of improving the crosslinking rate cannot be obtained, and 3 parts by weight! If the amount exceeds 50%, it becomes excessive and the electrical properties, mechanical properties, etc. of the crosslinked molded product deteriorate, which is not preferable. By incorporating a photosensitizer, the crosslinking efficiency can be significantly improved, making it possible to achieve a high level of crosslinking in a short period of time.

As a crosslinking aid, triallyl noanurate,
A compound having a hydrogen-accepting group such as triallylisonoanurate and N N'm phenylenethumaleimide is used to promote the crosslinking reaction between crystalline polyolefin molecules. The amount of this crosslinking auxiliary agent to be blended is usually preferably in the range of 0.3 to 4 parts by weight per 100 parts by weight of the crystalline polyolefin. If the amount is less than 0.3 parts by weight, the effect of these additions cannot be obtained sufficiently, and if it exceeds 4 parts by weight, it becomes excessive and is disadvantageous because it adversely affects the physical properties of the molded product after crosslinking.

In addition to the above-mentioned ultraviolet absorber, photosensitizer, and crosslinking aid, tetrakisulomethylene-3-(35'-)
Additives and fillers that do not impair transparency under the temperature conditions during irradiation, such as anti-aging agents such as butyl-4°-hydroquinophenyl)propionate comethane, may be appropriately blended. Furthermore, 44° foams under the temperature conditions during irradiation.
A foaming agent such as oxinobischenzenosulfonyl hydrazide or azonocarbonamide can also be added, and with this, a foamed crosslinked molded product can be produced.

In addition, as a means for molding a mixture of a crystalline polyolefin and an ultraviolet absorber, or a mixture to which a photosensitizer or a crosslinking aid is added, various methods conventionally used for molding crystalline polyolefins can be used. What can be applied? If the molded product is in the form of a sheet, film, tube, or pipe, extrusion molding using a normal extrusion molding machine can be used. Second, in the case of molded products or coverings such as electric wires and cables, such as insulators and north, the extrusion coating method using an extruder equipped with a cross-layer die or the method of winding tape are used. .

Furthermore, it may be made into a molded product using a normal injection molding method. However, in the case of molded products with complex shapes, it may be inappropriate to use UV irradiation because the shape will be distorted as the product is heated above the crystal melting point when irradiated with UV rays.
The molded product may have a complicated shape as long as the molded product is not housed inside a mold made of a material that is transparent to ultraviolet rays and has heat resistance, such as quartz glass.

Further, the upper limit of the wall thickness of the molded article is 10 to 15 mm if the molded article is sheet-like and can be irradiated with ultraviolet rays from both sides, and 5 to 8 mm if irradiated only from one side. Of course, if the intensity (energy density) and irradiation time of the ultraviolet rays are increased and the irradiation time is increased, a thicker molded product may be obtained, or the crystalline polyolefin will deteriorate at the same time due to the ultraviolet rays, so care must be taken.

Next, the molded article thus obtained is irradiated with ultraviolet rays at a temperature equal to or higher than the crystalline melting point of the crystalline polyolefin.

In principle, this temperature condition is above the crystal melting point, but
Preferably, the temperature is about 10 to 20°C higher than the crystal melting point. However, if the temperature is too high, the crystalline polyolefin will undergo thermal deterioration, which is undesirable. Molded item 1
In the case of a crystalline polyolefin containing more than one seed, the temperature condition is set to be equal to or higher than the highest crystal melting point.

Further, as the ultraviolet irradiation conditions, a radiation source with a wavelength not less than 200 nm is used.

For this purpose, a high-pressure mercury lamp (wavelength range 250-600 nm) is required.
m) or metal halide (wavelength range 200 to 600 nm) are suitable. In particular, metal halide lamps have a large spectrum on the long wavelength side of 350 nm or more, have good transparency, and are suitable for thick objects.

In addition, its strength (energy density) is 10-' to 10
A range of −6 in-neutine/am”·min is desirable.

The irradiation time varies depending on the crosslinking density, the thickness of the molded product, etc., and is usually about 10 to 60 seconds, but is not limited to this range. For example, if only the surface of the molded product is to be crosslinked, , it may be even shorter.

Furthermore, if the shape of the molded product is a flat plate such as a sheet or film, thick molded products can be crosslinked in a short time by placing ultraviolet light sources on both sides of the molded product. Also, electric wire,
In the case of a covering such as a cable, the light sources can be uniformly arranged outside the periphery so that the entire outer circumference 7 can be uniformly irradiated. In addition, when a coating is placed directly on a metal conductor such as copper, the surface of the metal conductor acts as a reflective surface to reflect the ultraviolet rays, allowing efficient use of the ultraviolet rays. In the case of hollow cylindrical objects such as tubes and pipes, it is possible to uniformly irradiate them from the outer periphery in the same way, and when the inner diameter of the hollow part is too large (L), the ultraviolet light source is placed inside the hollow part to irradiate the inside and outside. It may be irradiated at the same time. Furthermore, an ultraviolet light source may be placed close to the exit portion of the die of the extrusion molding machine, and the ultraviolet light source may be directly irradiated with ultraviolet light at a high temperature equal to or higher than the crystal melting point immediately after extrusion.

By irradiating ultraviolet rays under such conditions, for example, polyethylene can be crosslinked to a degree of crosslinking density of up to about 90%, and a polyethylene sheet with a thickness of about 3 mm can be crosslinked in 10 to 30 seconds.

The molded product after crosslinking is cooled by cooling means such as natural air cooling or water cooling to become a crosslinked molded product.

In this method of manufacturing cross-linked polyolefin moldings, the crystalline polyolefin is completely amorphous and transparent when irradiated with ultraviolet rays, so the ultraviolet rays are well absorbed and transmitted, reaching deep into the molded material. Crosslinking is performed by In addition, since the temperature is above the crystal melting point, the movement of polymer molecules becomes active, and the crosslinking reaction proceeds more quickly. Furthermore, if a photosensitizer is added, the sensitizing effect will improve the efficiency of light energy use and promote the crosslinking reaction, and if a crosslinking aid is added, the concentration of active groups will increase and the polymer molecular chain This will encourage a reaction between the two. In addition, due to the action of the ultraviolet absorber, the photodecomposition of the crystalline polyolefin itself due to ultraviolet rays is minimized, and although there is a slight decrease in the crosslinking rate, the coloring and mechanical strength of molded products due to photodecomposition are prevented. It can be prevented.

Hereinafter, specific examples will be shown to clarify the effects.

"Example" To 100 parts by weight of low density polyethylene with a melt index (Ml) of 10, 1 part by weight of 4-chlorohensiphenone as a photosensitizer and 1 part by weight of triallyl noanurate as a crosslinking aid were added, An insulator with a thickness of 3 mm is applied to a conductor with a cross-sectional area of 100 mm at a temperature of 160°C using an extruder.
coated with.

After extrusion coating, the insulator temperature was maintained at 350'C or higher, and the material was guided to each of the ultraviolet irradiation sections shown below, and after 20 seconds of irradiation with ultraviolet rays with an intensity of 1.5XIO-5 einneutaine/cm2-min. , lead it to a cooling tank and obtain an insulated wire.

■Low-pressure mercury lamp...Wavelength range 250 nm or less ■High-pressure mercury lamp...Wavelength range 250-600 nm ■Metal halide lamp...Wavelength range 250-600 nm ■High-pressure mercury lamp ↑ Phenyl salicylate 0.011Ii% toluene solution ■ In this method, phenyl salicylate, which is an ultraviolet absorber, is added before coating the insulator.

For insulated wires under each condition, the gel fraction of the outer layer, middle layer, and inner layer of the insulator and the degree of coloration of the surface indicating the state of deterioration due to ultraviolet rays were measured. The results are shown in Table 1.

From the results in Table 1, ultraviolet irradiation according to the present invention (■ to ■)
In this case, an appropriate gel fraction can be obtained, and deterioration due to ultraviolet rays can be suppressed to a level that is not a practical problem.

In particular, if a metal halide lamp is used, a relatively uniform Kel fraction can be obtained throughout the interior, and the effect of the ultraviolet absorber can also be observed.

As for the ultraviolet absorber, it is also possible to use it by kneading it into the insulator.

1. Effects of the invention - As explained above, the method for producing a crosslinked polyolefin molded product of the present invention involves producing a molded product made of a crystalline polyolefin at a temperature equal to or higher than the crystal melting point of the crystalline polyolefin.
Since it irradiates ultraviolet rays with a wavelength of 200 nm or more, it is possible to crosslink relatively thick polyolefin molded products efficiently, with high crosslinking density deep inside, and in a short time, as well as to form crystals. This can prevent the deterioration of the polyolefin itself due to ultraviolet rays.

In particular, the effect can be further enhanced by using a UV absorber in combination.

Claims (7)

[Claims] (1) A method for producing a crosslinked polyolefin molded product, which comprises irradiating a molded product made of a crystalline polyolefin with ultraviolet light having a wavelength of 200 nm or more at a temperature higher than the crystal melting point of the crystalline polyolefin. (2) A method for producing a crosslinked polyolefin molded product, which comprises irradiating a molded product made of a crystalline polyolefin and an ultraviolet absorber with ultraviolet light having a wavelength of 200 nm or more at a temperature equal to or higher than the crystal melting point of the crystalline polyolefin. (3) A crosslinked polyolefin characterized by irradiating a molded product made of a crystalline polyolefin, an ultraviolet absorber, and a photosensitizer with ultraviolet light having a wavelength of 200 nm or more at a temperature higher than the crystal melting point of the crystalline polyolefin. Manufacturing method for molded products. (4) A molded product consisting of a crystalline polyolefin, an ultraviolet absorber, a photosensitizer, and a crosslinking aid is irradiated with ultraviolet light having a wavelength of 200 nm or more at a temperature higher than the crystal melting point of the crystalline polyolefin. A method for producing a crosslinked polyolefin molded product. (5) Claim in which the molded product is a covering for electric wires or cables (
1) The method for producing a crosslinked polyolefin molded product according to any one of (4). (6) The method for producing a crosslinked polyolefin molded product according to any one of claims (1) to (4), wherein the molded product is a cylindrical object such as a tube or a pipe. (7) The method for producing a crosslinked polyolefin molded product according to any one of claims (1) to (4), wherein the molded product is in the form of a flat plate such as a film or a sheet.